dont let signed in users create new users.

content/signup.php

 
 Design::header($setup, 0);
 
+if (User::checkLogin() == true) {
+    header('Location: '.Config::$sys_url.'?page=home');
+}
+
 if (isset($_POST['username'])) {
     if (Alter::addUser($_POST['username'],$_POST['password'],$_POST['realname'],$_POST['mail'],25)) {
      // Success! User created - Redirect to login